The enteric facultative anaerobes, such asEnterococcus faecalis, are catalase-negative phenotypes and are deficient in heme biosynthesis. Although they also lack respiratory cytochromes, the S. faecalis utilizes oxygen to enhance growth yields. These organisms rely entirely on substrate-level phosphorylation for ATP synthesis and utilizes novel flavoenzymes as oxidoreductases. An understanding of the structural organization of many of the elements contributing to E. faecalis metabolism and regulation would give a clearer picture of their proliferative mechanism. The roles of these flavin-linked enzymes in enterococcal oxidative metabolism and their contribution to their proliferation may yield insight to novel approaches of limiting infection by these organisms.